Conventionally, there are known vehicles, such as motorcycles and ATVs (All Terrain Vehicles), of the type including a so-called AMT (automated manual transmission). See, for example, Japanese Patent Publication No. 2007-069638. The AMT is one type of clutch drive apparatuses that perform clutch engagement or disengagement by using the drive force of an actuator, such as an electric motor.
The AMT described in Japanese Patent Publication No. 2007-069638 includes an electric motor and a hydraulic master cylinder that is driven by the electric motor and causes a clutch to be engaged and disengaged. A hydraulic circuit is provided in a power transmission mechanism between the electric motor and the clutch. The AMT further includes an auxiliary spring that assists disengagement of the clutch performed by the electric motor.
For the AMT including the auxiliary spring, an idle amount of the clutch is set to attain a match between a neutral position where an assist force associated with the auxiliary spring is zero and a “meet point” position, which is a position where disengagement of the clutch is initiated. The idle of the clutch refers to a state where no load from the clutch is applied even after the initiation of rotation of the electric motor, and the idle amount of the clutch refers to the rotational speed of the electric motor until reaching the meet point from the initiation of rotation of the electric motor. In an AMT including a hydraulic circuit in a power transmission mechanism, the idle amount of a clutch is regulated on the side of the hydraulic circuit (for example, through regulation of the hydraulic pressure). Hence, the idle amount does not have to be regulated in a mechanical portion of the power transmission mechanism.
Also known is an AMT in which a hydraulic circuit is not provided in a power transmission mechanism located between a clutch actuator and a clutch. See in this regard, for example, Japanese Patent Publication No. 11-222043. However, the AMT described in Japanese Patent Publication No. 11-222043 does not include an auxiliary spring. In the AMT described in Japanese Patent Publication No. 11-222043, a clutch disengagement sensor for detecting disengagement of the clutch is provided in order to minimize the influence due to idling of the clutch is reduced to thereby enable, for example, reduction of the time necessary for performing a smooth transmission operation. However, in the case of the AMT described in Japanese Patent Publication No. 11-222043, the provision of clutch disengagement sensor while necessary leads to an increase in the number of components/parts and associated cost involved.